A light emitting diode comprises a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively.
In LED applications, an LED semiconductor chip includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which causes the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light. The ability of LED semiconductors to emit light has allowed these semiconductors to be used in a variety of lighting devices. For example, LED semiconductors may be used in general lighting devices for interior applications or in various exterior applications.
During manufacture, an array comprising a large number of LED semiconductor devices (or dies) are produced on a substrate. A molding process is used to mold encapsulations having a desired shape over each device. For example, the encapsulations may be lenses that comprise phosphor, silicone or other materials that are molded into a variety of shapes designed to extract light emitted from the LED devices.
There are several methods that can be use to create encapsulations from plastics or other materials. These methods include thermoforming, compression molding, transfer molding and injection molding. The first two are the simplest and oldest methods; the first one however is applicable only to thermoplastic materials which can be thermoformed using pressure and heat. The second one, namely compression molding, is widely used in the plastics industry as it is applicable to both thermoplastics and thermosets.
It is a well known trend that manufacturers try to avoid the compression molding technique due to its batch oriented nature and the necessity to clean off seams and flash from the molded product. For example cleaning the flash is largely a manual operation and is especially tedious, time consuming, and inefficient. Furthermore, cleaning the flash is even more difficult when the substrate is designed from flexible material and/or includes perforations, grooves, or gaps that are designed to facilitate separation of the devices from the substrate.
Accordingly, what is needed is a simple and efficient system to overmold encapsulations onto LED array substrates that reduces the time and manual operations necessary to clean seams and flash resulting from the molding process. The system should also work with flexible substrates having perforations, grooves or other features that typically make cleaning difficult and time consuming.